Demand for batteries has been increasing dramatically. With this increase, there is a need for high-energy batteries that use multiple electrochemical cells coupled together to provide higher current and high voltage outputs.
A multi-cell battery pack usually includes individual electrochemical cells connected in series to create a battery with a higher voltage. For example, four Lithium Ion (Li-Ion) electrochemical cells with a nominal voltage of about 3.6 volts may be connected in series to develop a multi-cell battery with a nominal voltage of about 14.4 volts. Two of these three-cell series-connected groupings may be connected in parallel to create a multi-cell battery including a total of six cells with twice the current capability at about 14.4 volts.
Electrochemical cells, particularly Li-Ion cells, can be damaged by excessive charge voltage or when discharged to too low of a voltage. Electrochemical cells can also be damaged by extremes in temperature on both the hot extreme and the cold extreme. Moreover, undesirable and unsafe reactions, such as cell venting, electrolyte leakage, smoke, fire, and cell rupture may occur without proper controls on environmental conditions, charging conditions, and discharging conditions.
Monitoring and controlling systems have been proposed to deal with some of these issues. However, these proposals generally monitor the condition of the overall multi-cell battery and disconnect the multi-cell battery if an adverse condition is detected.
FIG. 1 is a simplified circuit diagram of a conventional monitor and control circuit for a battery pack including multiple electrochemical cells. Electrochemical cells EC1, EC2, EC3, and EC4 are coupled in series to create a multi-cell battery 160 that can develop a voltage between a positive terminal (+Vbat) 140 and a negative terminal (−Vbat) 150. A battery monitor 100 is coupled to the positive terminal 140 and negative terminal 150 to determine whether the multi-cell battery 160 is within a desired voltage range during, for example, charging and discharging. A temperature sensor 120 is included to determine if the multi-cell battery 160 is in an acceptable temperature range. A controller 130 uses outputs from the temperature sensor 120 and voltage monitor 110 to determine whether to disconnect or connect the multi-cell battery 160 from the negative terminal 150 using switch S1. However, this conventional monitor and control circuit only operates on the multi-cell battery as a whole and doesn't give information or control at the individual electrochemical cell level.
There is a need to improve the overall safety and reliability of electrochemical cells arrayed together by monitoring and controlling the electrochemical cells at a cell level or a sub-array level.